Voice communication systems within companies and organizations are increasingly using packet-oriented methods for voice communication. Frequently a reason for doing so is to allow shared use of the cabling of an IP-based data network (IP: Internet Protocol) for coupling of data computers, as well as for coupling IP-based communication devices of the voice communication system—for example IP telephones, gatekeepers, gateways.
The use of IP-based principles gives rise, in the voice communication system, to problems which were previously only known in computer networks. Thus for example an IP telephone can be attacked by a computer virus, a computer worm or a denial-of-service attack and thus caused to malfunction. A firewall in the data network which can block unwanted data traffic usually provides protection against these types of attack. A firewall is however frequently not optimized for protection against attacks on IP telephones. Furthermore a firewall may not be configured too restrictively since the desired communication exchange should not be impeded.